The present invention relates to marine seismic exploration and more particularly to a sound source for conducting marine seismic explorations.
A common problem in marine seismic exploration is reception of horizontally travelling noise by the hydrophones in the marine streamer towed behind a survey vessel. The horizontally travelling noise is created by the seismic waves produced by the sound source striking features on the ocean floor and being reflected back to the hydrophones in the marine streamer. A suggested solution to this problem is contained in U.S. Pat. No. 3,491,848. This patent suggests that an array of seismic sources to streamed behind the exploration vessel with the sources being spaced apart in both the cross-line and in-line planes. In this manner, horizontally travelling noise signals of predetermined wave lengths arrive at the hydrophones as a result of sources disposed to one side of the marine streamer will be out of phase with horizontally travelling noise arriving as a result of sources disposed on the opposite side. The recorded data then is a composite of the desired seismic signal and the noise signals, which are reduced, since they are out of phase.
The above mentioned patent suggests various configurations and horizontal dispositions of sound sources for reducing or cancelling horizontally travelling noise. In all of the configurations the sources are attached to individual floats with the floats being secured to a tow cable. When one or more of the sources fail, the amplitude, frequency and direction of the seismic waves produced by the sources changes. These characteristics of the sources are normally referred to as the signature of the source. The signature of the source is determined from tests and used in deconvolving the recorded data to remove the effects of the source from the data. Any changes in the signature during the survey will produce errors in the processed data. Since the sources in the patent are connected to a common tow cable and disposed in particular configurations it is impossible to compensate or correct the source signature when one or more of the individual sources fail.